Version 6.2 637 February 2011
SIP User's Manual 10. Advanced PSTN Configuration
10 Advanced PSTN Configuration
This section discusses advanced PSTN configurations.
10.1 Clock Settings
In a traditional TDM service network such as PSTN, both ends of the TDM connection must
be synchronized. If synchronization is not achieved, voice frames are either dropped (to
prevent a buffer overflow condition) or inserted (to prevent an underflow condition). In both
cases, connection quality and reliability is affected.
PSTN line clock (see ''Recovering Clock from PSTN Line'' on page 637)
Internal cl
ock (see ''Configuring Internal Clock as Clock Source'' on page 638)
Note: When the device is used in a ‘non-span’ configuration, the internal device
clock must be used (as explained above).
10.1.1 Recovering Clock from PSTN Line Interface
This section provides a brief description for configuring synchronization based on
recovering clock from the PSTN line (Trunk) interface. For a full description of the clock
parameters, see ''PSTN Parameters'' on page 783.
TDMBu
sClockSource = 4 (‘Network’) - recovers clock from line interface
ClockMaster: configures the PSTN trunk to recover/derive clock from the device or
transmit the clock to the remote side of the PSTN trunk (i.e. clock slave or clock
master):
ClockMaster_x = 0/1 (where ‘x’ depicts the trunk number) - ‘0’ means to recover/derive
clock (i.e. slave); ‘1’ means to transmit/drive clock (i.e. master).
TDMBusLocalReference: selects the trunk from which the clock is derived.
TDMBusLocalReference = x (where ‘x’ is the trunk number and 0 is the first trunk -
default)
TDMBusPSTNAutoClockEnable: The device has an automatic mechanism to detect
when a “local-reference” trunk (set by TDMBusLocalReference) is no longer capable
of supplying the clock to the system, and can automatically switch to the next available
trunk (according to the priority set by the AutoClockTrunkPriority and
TDMBusPSTNAutoClockRevertingEnable parameters).
TDMBusPSTNAutoClockEnable = 1 (device automatically selects one of the
connected 'slave' trunks)
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